S-shaped electrical connecting and clamping strap



Sept. 1, 1953 R. T. ROTH 2,651,026

S-SHAPED ELECTRICAL CONNECTING AND CLAMPING STRAP Filed Jan. 24, 1950 applied through a bolt and nut.

Patented Sept. 1,1953

UNITED STATES PATENT OFFICE S-SHAPED ELECTRICAL CONNECTING AND CLAMPIN G STRAP Raymond T. Roth, Philadelphia, Pa.; Elsie Edwards Roth and Norman Klauder, executors of said Raymond T. Roth, deceased Application January 24, 1950, Serial No. 140,275

. 6 Claims. 1

This invention relates to clamps for connecting two objects to each other by means of pressure A clamp or connector constructed in accordance therewith is especially adapted for use between electrical cables or conductors and is an improvement in the connector described in my copending application Serial No. 735,624, filed March 19, 1947, now abandoned.

a A primary object of the present invention is to provide an improved nut and bolt construction for a clamp assembly.

A further object of the invention is to provide an improved electrical connector adapted particularly to join two electrical conductors of which has improved gripping features between the clamp and the conductors.

- A further object of the invention is to provide in an electrical conductor of the class'described, a clamp having increased electrical contact surface between the clamp'and the conductors.

A still further object of the invention is'to provide a clamp of the class described which may be more readily installed and in which'the torque necessary to provide suitable electrical contact is controlled within desired limits.

A still further object of the invention is to provide an electrical connector of the class described, having an improved construction for the nut and bolt head. 7

A still further object of the invention is to provide a clamp between electrical conductors of different metals in which any electrolytic action between the clamp and the conductors is reduced to a minimum or eliminated.

Further objects will be apparent from the specification and drawings in which:

v Fig. 1 is a side view showing one form of my improved clamp connector used between conductors of substantially the same diameter;

Fig. 2 is a view similar to Fig. 1, but showing a modified connector suitable for use between conductors of considerably clifierent diameters;

Fig. 3 is a transverse section of the in Figs 1 and 2;

nut shown Fig. 4 shows a clamp similar to Fig. l'used between two conductors of substantially equal but 2 smaller diameters, and employing a modified nut and bolt head;

Fig. 5 is a view similar to Fig. 4, showing a bimetallic strap for the clamp;

Fig. 6 is a side view of the strap shown in Fig. 1 before installation on the conductors;

Fig. 7 is a developed view or fiat plan of the strap shown in Fig. 6;

Fig. 8 is a transverse section as seen at 88 of Fig. '7 and I Fig. 9 is a transverse section as seen at Fig. 6.

The invention comprises essentially the provision of an S-shaped strap or band having an aperture or hole at either end and a central aperture which, when the strap is formed into the desired S-shape, is substantially in alignment with the holes in the ends of the strap. For an electrical connector, the strap is made of an electrically conductive material such as copper, which may be provided with suitable serrations for improved electrical contact between the strap and one or both electrical conductors. Also, I prefer to form the strap so that it is outwardly convex both transversely and longitudinally at the apex of each bend. A transverse slot may be milled or otherwise provided on the inside or concave portion of the bend to assist in the tightening of the strap and to insure ample electrical contact. The strap, if desired, may be of a bonded bi-metallic construction of metals such as copper and aluminum, in order to inhibit any electrolytic action therebetween. It is desirable that the diameter of the center strap hole be large enough to clear at least one-half of the tapered face of the nut. Also, the nut as well as the bolt head may be provided with a relatively short conical or semi-spherical face to prevent bottoming on the threads and also to permit the use of a partially smooth shank on the bolt.

The connector or clamp assembly described herein incorporates several innovations which are directed to the problem of securing proper and adequate pressure between the objects that are clamped together. While my clamp is primarily intended for use between electrical conductors, it will be understood that it may also be utilized to join bars, tubes, or rods for any purpose whatsoever.

Referring now more particularly to the drawings. a clamp constructed in accordance with the present invention comprises a bolt I0 having a hexagonal head II and a tapered frusto-conical surface l2 between the bolt head H and the bolt shank Hi. The bolt I0 is inserted through holes l4, l and IS in an s-shaped strap H to connect, for example, a pair of electrical conductors l8 and 19 which are enclosed by the bends Na and 11b of strap H. A nut 20 having an elongated rrusto-conical face is drawn up on bolt ill so that a wedging action takes place between face 2t of nut 2t and conductor 59, as wellas between face l2 of bolt head H and conductor 18. The diameter of holes l4 and i6 is such that the face I2 of bolt head II and the face 2! of nut 20, extend substantially halfway into these. holes. Consequently, as the ends of strap H. are. drawn around conductors i8 and i9, face i2 bears on opposite edges 22 and 25, of hole M2,. and. face:

2| bears on opposite edges: 2:5: and 2 5 of hole E5 so that there is a continuous and ample contact area between the strap ll and. both the bolthead and the nut, regardless of the amount that the nut may be run onto the threads 25 of: the bolt.

The strap ll shown in Figs. 1, 6 and 7, may be; used to clamp objects-having somewhat different diameters. However, in the event. that it is; desired to connect objects of; widely different diameters, it will be desirable to relocate one or more of the holes in the strap, as shown in Fig. 2. In this event, the nut 2% will or course, run onto threads 25 a greater distance than shown in Fig. 1, to obtain the desired tight wedging action between the small object or conductor 2'! and the nut 20. In order to reduce the number of different parts that may be required to connect objects of different diameters, I have provided the nut. 20- with a counterbore 253 (Fig. 3) so that it may be turned well onto the bolt iii before bottoming on the unthreaded shank 53'. The cost of providing threads on shank it of the bolt substantially all the way up to the tapered face [2, has been found to be prohibitive either witha rolled or with a cut thread, so that threads 26' terminatea substantial distance short of the face l2. This improved construction, of the nut provides an ample tapered surface for wedging the conductor over a wide variety of conductor sizes, and also permits a substantial reduction in cost tobe achieved by eliminating expensive and unnecessary threading on the. bolt shank. Furthermore, the unthreaded. portion of the. nut serves as a guide that enables the nut to be readily started onthe bolt threads with a minimum of effort and lost time due to dropping. Due to the fact that linemen ordinarily wear cumbersome rubber gloves, this thread sta-rting feature of the nut is quite beneficial.

In addition to the counterbore referredto above, a center strap hole i5 is of sufiic-ient diameter to permit the minimum diameter of the leading edge of nut 2%, to enter the center hole in the event that the nut must be turned on: the bolt unusually far in order to securely clamp one of the conductors.

Figs. 4 and 5 illustrate a slightly modified nut and bolt construction which may be employed with. objects of relatively small diameter. Referring to Fig. 4-, head 36 of bolt 3! has afrustoconical face 32 similar to the face i2 of bolt, head I l but which is relatively shorterand which does not extend so far through the end strap hole 33 of strap 34. Likewise, the nut 35 used. in conjunction with bolt 3! has a relatively short frusto-conical face 36 which seats in the. end strap hole 31. In both cases, the-minimum diameter. of. the tapered facesv is onlyslight-ly: less; than thediameters of the holes-.53 and'51l" so; that the faces at most extend only slightly through. the holes. Nut 35 may. also, if desired, becounterall times.

4 bored in the same manner as shown in conjunction with nut 20 so that the nut may be partially run over the unthreaded shank 38 of bolt 30.

Fig. 5 shows another modified bolt and nut configuration. In this case, the bolt head 40 has a semi-spherical face M which seats completely the end strap hole 42* of strap 43. Nut M likewise has a semi-spherical face. 55 which seats in the end strap hole 46. As in the case of Fig. 4, the minimum diameter of faces ll and 45 is. only slightly less than the diameter of holes:- 42 and 45. This insures that full contact between the strap and the bolt head, and between the. strap. and the nut, takes place at It: will be apparent that the size of the end strapholes, as well as the length and slope or the faces on the nuts and bolt heads, all cooperate to produce the desired result. The combined proportions however, should be such that the bolt head and nut when tight float in the strap, thus providing excellent electrical and/or mechanical contact with the clamped objects either withor without the wedging action.

Particularly in the case of an electrical connector, I provide the. straps H and 28 with trans.- verse slots or grooves and 5|: on the inside of the bends. These slots are-preferably narrower than the diameter of a singlestra-nd. ofthe. cable to be used for any of the conductors t8, L9, 2.1-, 54 or 55.. The depth of either slot. 50.- or 5t may be as great as one-half the thickness or"- the strap since it is only necessary: that one-half the current fiow past the slot, the other half. being transferred from the cable to the strap in the cable area between the slot and aperture I5. Since the cross-sectional area of the: straphas been substantially reduced at slots 50.- and.5l,- the torque required to tighten the nut is correspondingly reduced. Thus, with agiven amount of torque, greater wedging; action and. a better, electrical connection are achieved.

When. straps are pressed by the forming dies into the shape shown in Fig. 6, they may also be provided with serrations or grooves 52, 52 which tend to bite into the conductors and. therefore to improve the electrical connection between. the conductors and the strap. In addition, the bends of the straps, may be. transversely and outwardly convex (as shown. in Figs. 1, 2, 4, S and 9), so that there is. no tendency for the strap to bovv outwardly at. or near grooves. 5G, 5! when the nut. is tightened. This convexityv enhances the electrical connection between the conductors and the strap because otherwise the lateral. edges of the strap. tend topullaway from theconductors as the nut is drawn up. In other words, thestrap and. the conductor have. their maximum areas under pressure contact.

The present clamp construction also lends itself remarkably welltothe elimination of undesired electrolytic action when the clamp is used to. connect electric conductors. of different metals. When the connector is installed out.- doors or. where moistureris prevalent and therefore conduciveto electrolysis, I have found that a special bi-metallic strap 4.3 for my clamp enables anespecially beneficial result to-be realized. In this form for example, a layer" 55 of copper and a layer. 51 of aluminum may be: employed. It will be noted that. the. copper portion 55 of the strap. is. in contact with one conductor 58 and: with bolt head 40 (as shown; in Fig; 5). Similarly, the aluminum layer 51 of" the strap is incontact with the other conductor 59 and with the nut; 44; For optimum results of course,

the strap layer and the conductor with which it is in contact, should be of the same metal, so that in Fig. 5 conductor 59 is aluminum and conductor 58 is copper. These two metals are cited by way of example only, since other materials may be used with comparable results. It will thus be understood that all flow of electrical energy from one metal to a different metal takes place in the strap itself and the straps may be satisfactorily bonded in manufacture to reduce or avoid electrolysis. Alcuplate, a product of the General Plate Division of Metals & Controls Corporation, is an example of such a bi-metallic bonded material.

It will therefore be understood that I have provided an extremely satisfactory clamp for tightly clamping objects such as conductors. The clamp is relatively inexpensive to manufacture, is adapted to be utilized for a wide range of diameters, and the torque necessary to insure a suitably strong connection is relatively small, so that it is well within the Underwriters Laboratory requirements for clamp connectors. The shape of the strap enhances the ability to obtain full contact between the bends of the strap and the conductors. Also, the use of a bonded bimetallic strap which has an S configuration, is ideal for electrically uniting conductors of different materials. The construction of the bolt and nut is so designed that excellent contact under clamping conditions with a minimum of torque is provided even though the shank of the bolt is not completely threaded and also in the event that the nut must be turned relatively far onto the threaded portion.

Having thus described my invention, I claim:

1. A clamp assembly for joining a pair of electrical conductors and the like, comprising an S- shaped metal strap to extend about and embrace the conductors, said strap having an aperture in each end portion and an aperture in its central portion, the aperture in each end portion being defined by a circular wall extending perpendicularly to the faces of the strap, a bolt for insertion through said apertures having a threaded shank freely insertable through the apertures and a tapered portion engageable with the wall defining one of the end apertures, and a nut threadedly engageable with said shank and having a tapered portion engageable with the wall defining the other end aperture, whereby tight ening of the bolt and nut causes oblique positioning of the end portions of the strap relative to the axes of said tapered portions and effects biting line contact of each tapered portion with the associated wall completely about the tapered portion.

2. A clamp assembly according to claim 1, wherein each of the oppositely-facing bends of the S-shaped strap is provided on its inside with a transverse groove to increase the flexibility of each bend and thus enable easier tightening of the bolt and nut.

3. A clamp assembly according to claim 1, wherein each of the oppositely-facing bends of the S-shaped strap is outwardly convex transversely of the strap to effect better contact of the strap with each of said conductors.

4. A clamp assembly according to claim 1, wherein each of the oppositely-facing bends of the S-shaped strap is provided on its inside with serrations which bite into the associated conductor and thus efiect better contact therewith.

5. A clamp assembly according to claim 1, wherein said nut has an unthreaded bore extending inwardly from the smaller end of the tapered portion of the nut, said bore being of larger diameter than the threaded shank of the bolt, whereby the tapered portion of the nut may be projected inwardly beyond the thread on the bolt shank.

6. A clamp assembly according to claim 1, wherein said strap is composed of two different metals to prevent electrolytic action.

RAYMOND T. ROTH.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,205,733 Gutenkunst Nov. 21, 1916 1,487,617 Stoppenbach Mar. 18, 1924 1,894,327 Schellenger Jan. 17, 1933 1,940,617 Temple Dec. 19, 1933 1,986,642 Milne Jan. 1, 1935 2,017,421 Post Oct. 15, 1935 2,092,372 Goeller Sept. 7, 1937 2,295,051 Roth Sept. 8, 1942 2,381,331 Ayers Aug. 7, 1945 2,426,429 Bels Aug. 26, 1947 FOREIGN PATENTS Number Country Date 883,150 France June 24, 1943 

